1. Field of the Invention
The present invention relates generally to devices concerned with support of a person's body in a manner minimizing ischemic injury, more particularly to such devices utilizing a plurality of vertically oriented inflated cushions forming a substantially continuous surface underneath a patient's body providing buoyant support, and specifically to such devices which may be utilized upon a structure possessing inclined support surfaces such as a convalescent recliner.
2. General Background
Ischemia, which is commonly manifested by bed sores, is caused by vascular deformation which typically results from the internal pressure of interstitial fluid which characterizes swollen tissue. In order to avoid this condition, minimize the extent of the same and reduce the severity of developed ischemia, substantially uniform external pressure in the range of 20-80 mm Hg psig is desired. Localization of external pressure is, most importantly, to be avoided.
The prevention of ischemic ulcers, i.e. pressure sores, is perhaps best or most commonly achieved with a support surface which maximizes the distribution of external pressures. A support surface which conforms readily to the contours of a patient's body and which adjusts to changes in the tissues concerned over time promotes healing of ischemia by evenly distributing external pressure upon the body. Edema is reduced, over time, by moderate, evenly distributed, external pressure. Edema reduction returns capillarial proximity to afflicted tissue which, in turn, increases blood flow and nutrient supply to that tissue thereby reversing ischemia and ameliorating the deleterious effects of the same.
Discussion of the Prior Art
One of the most successful approaches to achieving the exertion of substantially equal external pressure upon a convalescent's body with a support surface which conforms and adjusts to the contours of those portions of that body contacted by said support surface is found in the utilization of a plurality of vertically oriented partially inflated cells positioned to contact each other horizontally. Devices of this type are economically manufactured by utilizing a form or mold of the type described in U.S. Pat. No. 3,870,450 entitled `Multicelled Structure Apparatus for Making Same` which discloses use of multiple fluted mandrels extending upward from a common base and which results in a plurality of fluted, vertically oriented pneumatic cells, either connected pneumatically or individually isolated, all disposed proximate each other such that moderate internal fluid pressure brings the cells into contact with each other horizontally and a substantially continuous support surface possessing the desirable characteristics described above is obtained.
Of course many other approaches are known including a number also considered pertinent to the present invention. U.S. Pat. No. 2,548,547 for a `Sectional Pad` issued Apr. 10, 1951 to Robert L. Melrose discloses use of a plurality of block shaped cushions peripherally flanged along the bottom presenting, along opposed edges, fastening elements oriented either upward or downward, permitting the joining of adjacent units together into an extensive pad and "selective removal of any unit thereby forming a hole extending completely through said pad" (Column 1, Lines 26-28). "(U)ndesirable pressure on any given portion of the body" is eliminated while providing "adequate and comfortable support to a reclining individual" (Column 1, Lines 15-18).
Use of pneumatic cells, horizontally disposed between a rigid base underneath and an elastomeric layer above, is disclosed by Albert E. Forsyth in U.S. Pat. No. 2,627,302 and No. 2,672,183. An additional layer of felt above the elastomeric is disclosed and upholstery fabric, peripherally fastened to the base, envelopes these several layers. A similar construction, also adapted for use on an inclined surface such as the back of a chair, is disclosed by Boyd S. Moore in U.S. Pat. No. 3,192,541 entitled `Contourable Pneumatic Cushions`. The plurality of laterally adjacent air cells each have a valve controlled connection to a common plenum which enables selective adjustment of the inflation of each relative to the others.
Clark Morrison and Charles F. Stoyka disclose a `Wheelchair Seating System` in U.S. Pat. No. 5,088,747 issued Feb. 18, 1992 which provides both the sling type horizontal seat support and the sling back of a collapsible chair having lateral rigid frame structures with a cushion inclusive of foam, gel, and felt like material with a removable rigid platform which straddles the opposed frame structures. Hook and loop material fasteners of the Velcro.TM. type are shown for holding the cushion to the sling seat or back while a board is optionally interposed therebetween.
Craig S. Miller, Sr. discloses an `Air Support Mattress Overlay With Fitted Sheet Mounting` in U.S. Pat. No. 5,745,941 issued May 5, 1998 which utilizes a pliable base sheet having a top and sides which fits retentively on top of a mattress. At least one air conduit comprised of "impermeable sheet material is layered on the base sheet" and supplies, preferably through snap type male and female fasteners along said conduit, transversely oriented inflatable elements which are removably fastened to the base sheet, preferably with said snap fasteners. This rather recently disclosed apparatus is intended to fulfill certain deficiencies in conventional inflatable overlay systems including a "complicated external tubing manifold" (Column 1, line 39) and, more interestingly with regard to the problems presently addressed, it is stated that:
Existing air support pad overlays lack a convenient means for attaching the overlay to the supporting mattress. Typically the overlay is attached by means of retaining straps engaged under the mattress. While this approach generally works, it is awkward and in some cases not entirely secure for keeping the overlay from shifting on the mattress. (Column 1, Lines 27-32)
Statement of Need
It is considered that a review of the pertinent prior art reveals two related concerns which have been inadequately addressed by the same. While support surfaces presented by partially inflated cells, particularly a plurality of vertically oriented cells in closed proximity, have been shown to be effective in ameliorating ischemia in the tissues of a convalescent's body contacted by the same, these structures are mainly intended for use as horizontal mattresses upon specially constructed beds, which are comparatively expensive in relation to ordinary or conventional beds. Inflatable overlays have a tendency to shift upon a conventional bed and wheelchairs present other difficulties.
Use of a fitted sheet has been disclosed as a means of preventing shifting of an inflatable overlay disposed upon a conventional bed which has an immobile horizontal support surface. Use of various pads attachable to the substantially horizontal seat and vertical back sling surfaces of a collapsible wheelchair has been disclosed. The interposition of a rigid surface, without attachment to either the pads or the sling structure, has been disclosed for the seat of such a system and implied for the back of the same though not shown. It is considered that the simple interposition of a board between a sling surface and a pad attached to the same would be problematic for the back because of the substantial inclination of the same from horizontal.
Convalescent recliners, mobile structures possessing three separate support surfaces each displaceable in a manner which obtains a range of inclination from nearly horizontal in those sections when fully reclined, are relatively neglected in the prior art. U.S. Pat. No. 5,715,548 for a `Chairbed` discloses a structure including three sections. Horizontally disposed inflatable elements are automatically pressurized by an electric pump and pressure sensor system included in one integral stand alone structure incompatible with any other conventional structure. This is regarded as necessarily very expensive in comparison with a conventional convalescent recliner which is wholly manual in operation.
It is therefore considered that a need exists for a patient support surface which is effective in countering ischemia and which is applicable to a conventional convalescent recliner possessing three separate sections two of which are capable of being inclined from a substantially vertical to nearly horizontal disposition, which is wholly manual, i.e. does not require electricity for operation. In short, a need is hence recognized for a simple, inexpensive, device which will provide relief from ischemia in support of a convalescent which may be variably inclined.